Soft x-ray mask alignment system

ABSTRACT

An alignment system for a soft X-ray lithographic system for aligning a mask with a substrate to be printed with a pattern including a first registration means on the mask and second registration means on the substrate; one of the registration means being a first soft X-ray absorber means of a predetermined form; the other registration means being a second soft X-ray absorber means having a space in it with the same predetermined form, and one of the registration means being carried over a soft X-ray transparent registration window on the mask, the other registration means being carried over a soft X-ray transparent registration window on the substrate.

United States Patent [1 1 Smith et a1.

[ June 26, 1973 SOFT X-RAY MASK ALIGNMENT SYSTEM [73] Assignee:Massachusetts Institute of Technology, Cambridge, Mass.

221 Filed: June 29,1972

211 Appl. No.: 267,667

Hallman 250/65 R 3,113,896 12/1963 Mann 250/49.5 TE

Primary ExaminerJames W. Lawrence Assistant Examiner-Harold A. DixonAttorney-Joseph S. Iandiorio and Arthur A. Smith,

[57] ABSTRACT An alignment system for a soft X-ray lithographic systemfor aligning a mask with a substrate to be printed with a patternincluding a first registration means on the mask and second registrationmeans on the substrate; one of the registration means being a first softX-ray absorber means of a predetermined form; the other registrationmeans being a second soft X-ray absorber means having a space in it withthe same predetermined form, and one of the registration means beingcarried over a soft X-ray transparent registration window on the mask,the other registration means being carried over a soft X-ray transparentregistration window on the substrate.

15 Claims, 17 Drawing Figures SOFT X-RAY MASK ALIGNMENT SYSTEM Theinvention herein described was made in the course of work performedunder a contract with the Department of Air Force, U. S. Department ofDefense.

FIELD OF INVENTION This invention relates to an alignment system forensuring that each soft X-ray mask in a set of such masks is properlyregistered with a substrate to be exposed and that each pattern on eachmask is properly 'positioned on that mask relative to the correspondingpatterns on the other masks of the set.

BACKGROUND OF INVENTION Recently soft X-ray lithography has beenproposed as a technique for replicating submicron resolution planarpatterns, Soft X-Ray Lithographic Apparatus and Process, Smith et al.,Ser. No. 217,902 filed Jan. 14, I972.

Soft X-ray masks have been fabricated with acoustic surface wavetransducer patterns with 1.3 micron electrode spacing and have beensuccessfully replicated. Thus soft X-ray lithography has shown aresolution capability greater than that of ordinary photolighography andcomparable to the scanning electron beam techniques. The simplicity andlow cost of soft X-ray lithography indicate that it would have asignificant impact in ultra-high resolution device fabrication in thefuture. However, in many fabrication procedures several masking stepsmay'bev required and the patterns produced by one mask must be preciselysuperimposed with respect to patterns produced by the other masks.However, the precision required is a great deal more than before; forthe previous mask replication techniques did not reproduce patternshaving elements in the submicron range and the scanning electron beamtechnique which did create patterns having elements in the submicronrange did so by tracing each pattern individually, not by a process ofmask replication, so that no mask registration was necessary. Each maskin a set of masks required to fabricate a complete circuit or device ona substrate must have its pattern properly positioned with submicronprecision related to the corresponding pattern on each of the othermasks of the set. Otherwise although the mask and substrate may beproperly registered the pattern may be out of alignment with a patternor patterns previously replicated in the same pattern area.

SUMMARY OF INVENTION It is therefore an object of this invention toprovide an alignment system for a soft X-ray lithographic system whichis capable of submicron precision compatible with that of the soft X-raylithographic replication and which is simple, inexpensive and readilymakes use of the soft X-rays available from the soft X-ray lithographicopcrations.

It is a further object of this invention to provide such an alignmentsystem which provides for precise registration of each mask in a set ofmasks with a substrate to be exposed.

It is a further object of this invention to provide such an alignmentsystem which ensures that each pattern on each mask in a set of masks isproperly positioned on that mask relative to the corresponding patternson the other masks of the set.

The invention results from the realization that for effective use ofsoft X-ray lithographic techniques an alignment system is absolutelyessential and that because of the high precision i.e. very small patternelements in the micron range, obtained with such techniques a highprecision alignment system is also essential and more importantly canbest be made using the soft X-rays available from the soft X-raylithographic operation.

The invention features an alignment system for a soft X-ray lithographicsystem for aligning a mask with a substrate to be printed with apattern. There is a first registration means on the mask and secondregistration means on the substrate. One of the registration means is afirst soft X-ray absorber means having a predetermined form; the otherof said registration means is a second soft X-ray absorber means havinga space in it of the same predetermined form. One of the registrationmeans is carried over a soft X-ray transparent registration window onthe mask and the other registration means is carried over a soft X-raytransparent registration window on the substrate.

DISCLOSURE OF PREFERRED EMBODIMENT- Other objects, features andadvantages will occur from the following description of a preferredembodiment and the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view of a master mask having registrationmeans and bench mark means according'to the alignment system of thisinvention;

FIG. Zis a diagrammatic, elevational, cross-sectional view taken alonglines 22 of FIG. 1;

FIG. 3 is a diagrammatic cross-sectional view illustrating exposure ofthe electron sensitive resist material using a scanning electron beammicroscope to produce the registration means and bench mark means on themaster mask;

FIG. 4 is a diagrammatic, elevational view of the master mask shown inFIG. 3 after the exposed resistive material has been developed;

FIG. 5 is a diagrammatic, elevational, cross-sectional view of themaster mask after a soft X-ray absorber material has been deposited inthe developed areas and the remaining portions of the electron sensitiveresist material have been dissolved away;

FIG.'6 is a diagrammatic, cross-sectional, elevational view showing theuse of soft X-rays to create a pattern mask from the master mask;

FIG. 7 is a diagrammatic, cross-sectional, elevational view of thepattern mask of FIG. 6 after the exposed portions of the resistivematerial have been developed;

FIG. 8 is a diagrammatic, cross-sectional, elevational view of thepattern mask of FIG. 7 after a soft Xray sbsorber has been deposited inthe developed areas and the remaining soft X-ray resistive material hasbeen dis- 7 solved away;

tern mask to create registration means on a substrate;

FIG. 13 is a diagrammatic, cross-sectional, elevational view of thesubstrate of FIG. 12 after the exposed portion has been developed andreplaced by a soft X-ray absorber material and the unexposed portion hasbeen dissolved;

FIG. 14 is a view of the substrate of FIG. 13 after windows have beenetched in it beneath the registration means;

FIG. 15 is a plan view of the substrate of FIG. 14;

FIG. 16 is a diagrammatic, cross-sectional, elevational view of a softX-ray lithographic system using an alignment system according to thisinvention to obtain proper registration between a pattern mask and asubstrate to be printed; and

FIG. 17 is a diagrammatic, axonometric view of a pattern mask having amultiplicity of pattern areas which uses registration means and benchmark means according to the alignment system of this invention.

The invention may be accomplished using a master mask which carries onit alignment means including at least two registration means and a benchmark means for each pattern which is to be produced on a substrate. Theregistration means and bench mark meansz'are produced on the master maskusing scanning electron beam microscope techniques and each of thealignment means has a predetermined form defined in a soft X-rayabsorber material located on a transparent portion of the master mask.Similarly each of the bench mark means has a predetermined form definedin soft X-ray absorber material carried on soft X-ray transparentportions of the master mask. Using soft X-ray lithographic techniques aset of pattern masks is created by exposure to soft X-rays through themaster mask. Each of the resulting pattern masks contains one or moreregistration means which are similar to the registration means on themaster mask. Each of these registration means may be either a positiveor a negative of the predetermined form that the registration meanstakes on the master mask. Similarly each of the pattern masks contains anumber of bench mark means corresponding to the bench mark means on themaster mask and each of these bench marks may also be either a positiveor negative of the respective bench mark means on the master mask.Associated with each of these bench mark means on the pattern mask is apattern area. A pattern is fabricated'in each of these areas on each ofthe pattern masks using scanning electron beam microscope technology. Bythe use of the bench marks as a starting point the scanning electronbeam microscope can precisely lay down a pattern on a mask and lay downcompatible patterns at the same relative position on each of the otherpattern masks in the set. Thus each of the plurality of the patternswhich must be printed on a pattern location on a substrate in order toproduce the final whole pattern is precisely aligned with each of theother patterns on each of the other pattern masks which must besuccessively applied to that substrate. The registration means createdon the substrate will be of the same form as those on the master maskand on each of the pattern masks but they will be the obverse of thoseon the pattern mask so that when the registration means on anyparticular pattern mask are in proper registration with the registrationmeans on the substrate no soft X-rays can penetrate that area of thepattern mask and substrate. Thus soft X-ray sensors may be used to senseany soft X-rays coming through registration has occureed. Aservo-mechanism using one or more piezoelectric drive units may be usedto move the substrate and pattern masks relative to one another toobtain a null indication which represents precise registration. Whenregistration has been achieved the pattern carried on each of thepattern locations on the pattern mask aligned with the substrate is thenprinted on the substrate using soft X-ray techniques. After the printingwith the first pattern mask has been accomplished that mask may beremoved and a second pattern mask put in its place and brought intoproper registration with the substrate and the second set of patterns isapplied to the pattern locations on the substrate. Operation continuesin this way until each of the individual patterns carried by each of thepattern masks has beenapplied to each of the corresponding locations onthe substrate and an entire pattern has been fabricated in each of thepattern locations on the substrate. The details of soft X-raylithography techniques may be obtained from co-pending application SoftX-Ray Lithographic Apparatus and Process, Ser. No. 217,902, filed'Jan.14, 1972 by Henry I. Smith, David L. Spears and Ernest Stern.

The etching techniques used to produce relatively transparent portionsor windows in the various masks and substrates is explained in moredetail in the copending application entitled Soft X-Ray Mask SupportSubstrate filed on even date herewith by David L. Spears, Henry I. Smithand Ernest Stern.

There is shown in FIG. 1 a master mask 10 having alignment meansincluding two registration means 12 and l4'and two bench mark means 16and 18. Typically each mask has two registration means and each patternarea has associated with it one bench mark means. Thus in FIG. 1 wheremaster mask 10 is shown designed to carry two pattern areas 20, 22 thereare two bench mark means 16 and 18. Each of registration means 12 and 14includes a layer of soft X-ray absorber material 24 which has an openspace 26 in it that defines the form 28 of the registration mark 25. Inthis case, the form 28 of registration mark takes the shape of an objectwith four salient points.

Similarly bench mark means 16 and 18 each includes a layer 30 of softX-ray absorber material. The bench mark 32 is formed by four spaces 34,which define the form 36 of a Greek cross without the center portion.Each of registration means 12 and 14 and each of bench mark means 16 and18 is carried on transparent portions of master mask 10 over windows 40,42 and 44 and 46, respectively, FIG. 2. The membrane 48, 50, 52 and 54in each of windows 40, 42, 44 and 46 is quite thin and thus transparentto soft X-rays; whereas the remaining areas of master mask 10, which aremuch thicker, are relatively opaque to soft X-rays.

Master mask 10 may be made beginning with a wafer 60, FIG. 3, of siliconwhich has been doped to a depth of a few microns with boron to form aboron diffusion layer 62. Wafer 60 is then covered on one surface by aprotective layer 64 of, for example, silicon dioxide and on its othersurface with a layer 66 of polymethyl methacrylate which is sensitive toelectron beam exposure. Wafer 60 is then submitted to a scanningelectron beam microscope 68 which traces the required patterns on layer66 to provide registration means 12 and 14 and bench mark means 16 and18. Wafer 60 is then subjected to a developer such as a solution of 40percent methyl isobutyl ketone and 60 percent isopropyl alcohol toremove the exposed portions 67 of layer 66 that now define registrationmeans 12 and 14 and bench mark means 16 and 18.

The various holes 70, FIG. 4, remaining in layer 66 are then filled witha soft X-ray absorber material such as by evaporation coating with gold.The remaining portions of layer 66 are then removed by dissolving themwith a solution of trichloroethylene. The remaining portions of softX-ray absorber material 24, FIG. 5, now define the registration mark 25of the registration means 12 and 14, and the soft X-ray absorbermaterial 30 defines the bench mark 32 in bench mark means 16 and 18.Openings 72, 74, 76 and 78 are etched in layer 64 using an etch such asbuffered hydrofluoric acid which attacks the silicon dioxide of layer 64but not the silicon of wafer 60. Wafer is now prepared to have windows40, 42, 44 and 46, FIG. 2, etched in it. An etchant which does notattack the remaining portions of the silicon dioxide layer 62 but doesattack the open areas of silicon wafer 60 at openings 72, 74, 76 and 78may be used. This may be accomplished using a 115 C. solution of 68 mlethylene diamene, 12g pyrocatechol, and 32 ml water, for about 1% hours.This etchant performs well on silicon wafer 60 but does not attack theboron diffused layer 62. Thus, as shown in FIG. 2, windows 40, 42, 44and 46 are created with thin membranes 48, 50, 52 and 54, respectively,covering them. This technique is described in detail in the applicationSoft X-Ray Mask Support Substrate by David L. Spears, Henry I. Smith andErnest Stern filed on even date herewith.

The completed master mask 10, FIG. 2, may now be used as in FIG. 6 tocreate a set of pattern masks one of which, pattern mask 80, includes awafer 82 of silicon containing a boron diffusion layer 84 similar tothat discussed, supra. Wafer 82 carried a layer 86 of soft X-raysensitive material such as polymethyl methracrylate on one surface and aprotective layer 88 of material such as silicon dioxide on its othersurface. Layer 86 is exposed to soft X-rays 91 from soft X-ray source 90through windows 40, 42, 44 and 46 in master mask 10 so that theregistration means 12 and 14 and the bench mark means 16 and 18 aredefined on layer 86. The exposed portions 92 of layer 86 are thensubjected to a developer such as a solution of 40 percent methylisobutyl ketone and 60 percent isopropyl alcohol to remove the exposedportions 92 of layer 86 leavingholes 94, FIG. 7, in their place. Holes94 are filled with a soft X-ray absorber material such as gold and theremaining portions of layer 86 are then removed by dissolving them witha solution of trichloroethylene leaving a layer of soft X-ray absorbingmaterial 96, FIG. 8, which constitutes a second set of registrationmeans 12' and 14' which are similar to the original registration meansI2 and 14 on master mask 10, FIG. 1.

Registration means 12' and 14', FIG. 9, on pattern mask 80 have the sameform 28' as registration means 12 and 14 except that in this case theregistration mark 25' is defined by the soft X-ray absorber material 24'itself, not, as in the case of registration means 12 and 14, by thespace 26 surrounded by the soft X-ray absorber layer 24. Similarly,bench mark means 16 and 18 include bench marks 32 whose form is definedby soft X-ray absorber layer 30 which actually fills spaces 34 to definethe form 36 of bench mark 32' as compared with bench mark 32 wherein theform 36 was defined by the soft X-ray absorber layer 30 surroundingspaces 34. Although in FIGS. 1-9 it is indicated that master mask 10 hasone variation of the registration marks and bench marks which mayarbitrally be designated as positives and the pattern mask hasregistration marks and bench marks which may be designated negatives,i.e. marks 25', 32' are the negatives or the obverse of marks 25 and 32,this is not a necessary limitation of the invention. For example, if anegative resist were used in place of the polymethyl methacrylate layer86 then marks 25' and 32' would be positives of marks 25 and 32.

Pattern areas 20 and 22 on pattern mask 80 may now be imprinted withpatterns and 102, FIG. 10, using a scanning electron beam microscopeguided by bench mark means 16' and 18' in a similar manner as discussedwith reference to FIGS. 3-5 and as explained in more detail inco-pending application Soft X-Ray Lithographic Apparatus and Process,Ser. No. 217,902, filed Jan. 14, 1972 by Henry I. Smith, David L. Spearsand Ernest Stern. Holes 104, 106, I08 and may now be created in silicondioxide layer 88 in the same manner as discussed previously withrelation to layer 64. Windows 112, I14, 116 and 118, FIG. 11, are thenetched in wafer 82 as discussed supra, leaving soft X-ray transparentmembranes 120, 122, 124 and 126.

A substrate 130, FIG. 12, on which a pattern is to be. constructed isprepared from a silicon wafer 132 having a layer 134 of soft X-raysensitive material such as polymethyl methacrylate on one surface and aprotective layer 136 such as silicon nitride on the other surface. Layer134 is then exposed to soft X-rays 91', FIG. 12, through a pattern mask80. In this operation the pattern areas 100 and 102 are not exposedsince it is only required to produce alignment means on the substrate130. Some means, such as soft X-ray opaque elements 138, 140 may be usedto cover windows 116 and 118 in pattern mask 80 to prevent the patterns100 and 102 from being patterned onto layer 134. However, soft X- raysfrom soft X-ray source 90' do pass through windows 112 and 114 throughthe registration means 12' and 14' and expose portions 142 of layer 134.The exposed portions 142 are removed by dissolving them with 40 percentmethyl isobutyl ketone and 60 percent isopropyl alcohol and are replacedwith soft X-ray absorber material; then the remaining unexposed portions141 of layer 134 may be dissolved in trichloroethylene leaving onlyregistration means12" and 14", FIG. 13. Windows and 152, FIG. 14, maynow be created in wafer 132 by attacking the silicon with an etchantsuch as a combination of hydrofluoric and nitric acid or a combinationof hydrofluoric acid, nitric acid and acetic acid. With these etchantsthe etching will be stopped substantially short of the other surface bymeans of a neutralizing bath. In the case of substrate 130 a lessselective etchant may be used because maximum transparency through theuse of a very thin membrane is not absolutely necessary as will be seensubsequently. Registration means 12" and 14" on substrate 130, FIG. 15,include a layer 24" of soft X-ray absorber material in which iscontained a space 26" having the form 28" of registration mark 25".Since pattern mask 80 is flipped over to print on substrate 130 thearrangement of the negative means on substrate 130 is a mirror image ofthat on pattern mask 80. Registration means 12" and 14" are the obverseof registration means 12' and 14' and are the same as registration means12 and 14. But the latter of this particular set of relationships is notessential to the invention. However, it is important that registrationmeans 12" and 14" be the obverse of registration means 12 and 14',whether or not either set of registration means 12', 14' or 12", 14" arethe same or the obverse of the original registration means 12 and 14 onmaster mask 10. Substrate 130, FIGS. 14 and 15, carries two patternareas and 22" but no bench marks as the final alignment re quires thatonly each successive pattern mask be properly aligned with the substrate130 during exposure. Previously each of the patterns on each of thepattern areas such as 20' has been created using the bench mark means asa guide for the scanning electron beam microscope so that each patternon the pattern areas on each of the succeeding pattern masks is properlyaligned with respect to each of the patterns in the same location oneach of the other pattern masks of the set.

In operation substrate 130, FIG. 16, is coated with a layer 160 of softX-ray sensitive material such as polymethyl methacrylate and issubjected to soft X-rays 91" from a soft X-ray source 90" through apattern mask 80. Soft X-rays 91" from soft X-ray source 90" pass throughwindows 112 and 114 in pattern mask 80 only in the areas not blocked bythe soft X-ray absorber material 24'. The soft X-rays which are notblocked by soft X-ray absorber material 24 then pass through substrae130 in the areas not blocked by soft X-ray absorber material 24". Thuswhen pattern mask 80 and substrate 130 are aligned the soft X-rayabsorber materials 24" and 24' are also precisely aligned so that nosoft X-rays will pass through substrate 130 and soft X-ray sensor 170will sense no soft X-rays. As a result a null point will be detected bynull detector 172 and an indication thereof will be submitted to control174. A duplicate system including soft X-ray sensor 170' and nulldetector 172 is associated with registration means 14' and 14". Control174 may be used to develop signals to drive orthogonally orientedpiezoelectric drives 175, 175 such as are available from Coherent OpticsInc. (Model 44 Electro-Micrometer) which are capable of moving substrate130 very small dis tances, in the order of microns, required for theprecise alignment of pattern mask 80 and substrate 130.

In operation the soft X-rays 91" passing through windows 116 and 118 ofpattern mask 80 would be blocked prior to the registration operation.Once proper registration is accomplished the blockage would be removedand the soft X-rays passing through windows 116 and 118 about thepatterns 100 and 102 would create an exposure pattern in layer 160 whichcould then be developed and further etched or processed by other meansknown in the art. After this operation is complete the next pattern maskof the set would be introduced in place of pattern mask 80 and the nextpattern would be laid down in areas 20" and 22" until all the patternsrequired to make a complete pattern in areas 20" and 22" have beenreproduced on substrate 130.

Typically the substrate made according to this invention would have amultiplicity of pattern areas on it and would require a pattern maskhaving a similar multiplicity of pattern areas and bench mark means.Thus in FIG. 17 a typical pattern mask 80 includes 42 separate patternareas 180 each of which has associated with it a bench mark means 182.Also included are two registration means 184 and 186. Pattern mask istypically 1 inch square and each of the 42 pattern areas isapproximately 65 mils square in area.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:

1. An alignment system for a soft X-ray lithographic system including aregistration system for registering a mask with a substrate to beprinted with a pattern comprising a first registration means on saidmask and second registration means on said substrate, one of saidregistration means being a first soft X-ray absorber means of apredetermined form, the other of said registration means being a secondsoft X-ray absorber means having a space in it of said predeterminedform and one of said registration means being carried over a soft X-raytransparent registration window on said mask, the other registrationmeans being carried over a soft X-ray transparent registration window onsaid substrate, one of said registration means being the obverse of theother.

2. The alignment system of claim 1 in which said predetermined formincludes four salient portions.

3. The alignment system of claim 2 in which said salient portions arearranged in spaced pairs on transverse axes.

4. The alignment system of claim 1 further including a soft X-raydetector for detecting soft X-rays passing about said first soft X-rayabsorber means and through the space in said second soft X-ray absorbermeans, and a first null detector means for determining when said firstabsorber means blocks the space in said second absorber means indicatingthat said mask and substrate are in registration.

5. The alignment system of claim 4 further including a piezoelectricpositioning device responsive to said first null detector means formoving said mask and substrate relative to one another to provide properregistration of said first registration means.

6. The alignment system of claim 1 in which there are at least two setsof first and second registration means on each mask and substraterespectively.

7. The alignment system of claim 1 further including a benchmark systemfor properly positioning each pattern, on each mask in a set of masks,relative to the corresponding patterns on the other masks of the set,said benchmark system including a benchmark of predetermined formdefined in first material.

8. The alignment system of claim 7 in which said benchmark ofpredetermined form includes four salient portions.

9. The alignment system of claim 8 in which said salient portions arearranged in spaced pairs on transverse axes.

10. The alignement system of claim 7 in which said predetermined form isdefined by a space surrounded by a first material.

11. An alignment system for a soft X-ray lithographic system comprising:

a master mask having at least a first registration means of a first formin soft X-ray absorber material carried on a soft X-ray transparentportion of said master mask;

a number of pattern masks each having on a soft X-ray transparentportion one second registration means for each of said firstregistration means, said second registration means including a secondform similar to said first form in soft X-ray absorber material; and

a substrate to be exposed through said pattern mask and having one thirdregistration means for each of said second registration means, saidthird registration means including a third form obverse to said secondform in soft X-ray absorber material.

12. The alignment system of claim 11 further including a soft X-raydetector for detecting soft X-rays passing about said second and thirdregistration means, and null detector means for determining when saidsecond and third registration means block transmission of soft X-raysindicating that said mask and substrate are in registration.

13. The alignment system of claim 11 further including a benchmarksystem for properly positioning each pattern, on each mask in a set ofmasks, relative to the corresponding patterns on the other masks of theset, said benchmark system including a plurality of first benchmarkmeans, one for each pattern to be exposed, carried on said master maskon a soft X-ray transparent portion, and a pluralityof second benchmarkmeans, one for each pattern to be exposed, carried on each of saidpattern masks.

14. A method of producing a soft X-ray alignment system for alignment ofa soft X-ray mask and substrate comprising:

on a soft X-ray transparent portion of a master mask generating a firstregistration means of a first form in soft X-ray absorber material;

generating from said master mask on each ofa plurality of pattern masksa second registration means of a second form similar to said first formin soft X-ray absorber material on a soft X-ray transparent portion; and

generating on a substrate third registration means obverse to saidsecond form'for alignment with respective ones of said second forms onsuccessive ones of said pattern masks.

15. A method of producing a soft X-ray alignment system for alignment ofa soft X-ray mask and substrate comprising:

generating on a soft X-ray transparent portion of a master mask a firstregistration means of a first form in soft X-ray absorber material;

generating on a soft X-ray transparent portion of a master mask a firstbenchmark means of a second form in soft X-ray absorber material;

generating from said master mask on each of a plurality of pattern maskssecond registration means of a third form similar to said first form insoft X-ray absorber material on a soft X-ray transparent portion;

generating from said master mask on each of said plurality of patternmasks second benchmark means of a fourth form similar to said secondform.

1. An alignment system for a soft X-ray lithographic system including aregistration system for registering a mask with a substrate to beprinted with a pattern comprising a first registration means on saidmask and second registration means on said substrate, one of saidregistration means being a first soft X-ray absorber means of apredetermined form, the other of said registration means being a secondsoft X-ray absorber means having a space in it of said predeterminedform and one of said registration means being carried over a soft X-raytransparent registration window on said mask, the other registrationmeans being carried over a soft X-ray transparent registration window onsaid substrate, one of said registration means being the obverse of theother.
 2. The alignment system of claim 1 in which said predeterminedform includes four salient portions.
 3. The alignment system of claim 2in which said salient portions are arranged in spaced pairs ontransverse axes.
 4. The alignment system of claim 1 further including asoft X-ray detector for detecting soft X-rays passing about said firstsoft X-ray absorber means and through the space in said second softX-ray absorber means, and a first null detector means for determiningwhen said first absorber means blocks the space in said second absorbermeans indicating that said mask and substrate are in registration. 5.The alignment system of claim 4 further including a piezoelectricpositioning device responsive to said first null detector means formoving said mask and substrate relative to one another to provide properregistration of said first registration means.
 6. The aLignment systemof claim 1 in which there are at least two sets of first and secondregistration means on each mask and substrate respectively.
 7. Thealignment system of claim 1 further including a benchmark system forproperly positioning each pattern, on each mask in a set of masks,relative to the corresponding patterns on the other masks of the set,said benchmark system including a benchmark of predetermined formdefined in first material.
 8. The alignment system of claim 7 in whichsaid benchmark of predetermined form includes four salient portions. 9.The alignment system of claim 8 in which said salient portions arearranged in spaced pairs on transverse axes.
 10. The alignement systemof claim 7 in which said predetermined form is defined by a spacesurrounded by a first material.
 11. An alignment system for a soft X-raylithographic system comprising: a master mask having at least a firstregistration means of a first form in soft X-ray absorber materialcarried on a soft X-ray transparent portion of said master mask; anumber of pattern masks each having on a soft X-ray transparent portionone second registration means for each of said first registration means,said second registration means including a second form similar to saidfirst form in soft X-ray absorber material; and a substrate to beexposed through said pattern mask and having one third registrationmeans for each of said second registration means, said thirdregistration means including a third form obverse to said second form insoft X-ray absorber material.
 12. The alignment system of claim 11further including a soft X-ray detector for detecting soft X-rayspassing about said second and third registration means, and nulldetector means for determining when said second and third registrationmeans block transmission of soft X-rays indicating that said mask andsubstrate are in registration.
 13. The alignment system of claim 11further including a benchmark system for properly positioning eachpattern, on each mask in a set of masks, relative to the correspondingpatterns on the other masks of the set, said benchmark system includinga plurality of first benchmark means, one for each pattern to beexposed, carried on said master mask on a soft X-ray transparentportion, and a plurality of second benchmark means, one for each patternto be exposed, carried on each of said pattern masks.
 14. A method ofproducing a soft X-ray alignment system for alignment of a soft X-raymask and substrate comprising: on a soft X-ray transparent portion of amaster mask generating a first registration means of a first form insoft X-ray absorber material; generating from said master mask on eachof a plurality of pattern masks a second registration means of a secondform similar to said first form in soft X-ray absorber material on asoft X-ray transparent portion; and generating on a substrate thirdregistration means obverse to said second form for alignment withrespective ones of said second forms on successive ones of said patternmasks.
 15. A method of producing a soft X-ray alignment system foralignment of a soft X-ray mask and substrate comprising: generating on asoft X-ray transparent portion of a master mask a first registrationmeans of a first form in soft X-ray absorber material; generating on asoft X-ray transparent portion of a master mask a first benchmark meansof a second form in soft X-ray absorber material; generating from saidmaster mask on each of a plurality of pattern masks second registrationmeans of a third form similar to said first form in soft X-ray absorbermaterial on a soft X-ray transparent portion; generating from saidmaster mask on each of said plurality of pattern masks second benchmarkmeans of a fourth form similar to said second form.